1. Field
The present invention relates generally to helicopters, vertical take-off and landing (VTOL) aircraft, and other rotorcraft which utilize horizontally disposed rotors to provide lift, and more specifically to such rotorcraft which utilize pairs of counter-rotating rotors to offset engine torque rather than a vertically disposed tail rotor.
2. State of the Art
Helicopters, VTOL aircraft, and other rotorcraft which are capable of vertical take-offs and landings are well known in the prior art. Extensive research and development has particularly been conducted particularly regarding helicopters over the last few decades. Advances in the area of drive systems, rotors, aerodynamics, and the like have made the helicopters a reliable form of transportation particularly used in the various branches of the military and the Coast Guard.
Conventional helicopters develop lift or vertical thrust during flight by continuously driving air downwardly using a single horizontally disposed main rotor which includes on a main rotor shaft with two or more radially extending airfoil shaped main rotor blades extending from a rotor head or central hub affixed to the upper end of the main rotor shaft. The vertical thrust generated by the main rotor is controlled by increasing or decreasing the rotational speed of the main rotor and by adjusting the pitch of the main rotor blades using a swash plate type pitch control mechanism disposed at the hub. A tail rotor of a much smaller size having two or more radially extending airfoil shaped blades is vertically disposed aft of the main rotor to offset engine torque which otherwise causes the fuselage of the helicopter to rotate in an opposite rotational direction from that of the main rotor. The tail rotor is typically driven at a constant rotational speed relative to the main rotor. Therefore, the pitch of the tail rotor blades is adjustable to provide the required horizontal thrust to resist engine torque rotating the main rotor and to provide directional control of the helicopter. Horizontal thrust to propel the helicopter forward, rearward, and sideways is achieved by changing the pitch angle of the blades during rotation about the fuselage of the helicopter using the pitch control mechanism.
Helicopters have been developed which utilize a pair of counter-rotating main rotors which offset the engine torque such that the tail rotor may be eliminated. Such helicopters include those with rotors having separate vertical axes of rotation which are longitudinally displaced on the fuselage such as used in the military. Others have rotors which are laterally displaced with axes of rotation. Some such helicopters have rotors which are completely separated in non-overlapping manner. Others have rotors that are tilted slightly laterally off vertical with blades that overlap. The blades are timed to interleave during rotation so as not to collide. Some helicopters have rotors which have a common vertical axis of rotation, which are hereinafter referred to as rotorcraft.
An example of a helicopter having rotors which are laterally displaced is disclosed in U.S. Pat. No. 4,771,967 issued to Geldbaugh. The helicopter has a pair of laterally displaced rotors which rotate in opposite directions. A wing structure is disposed above and below the blades which forms a leading edge ahead to the rotors to shelter the portion thereof moving with the air stream when the helicopter is in forward flight. A compressed gas ejection system aids in the transition of respective blades of the rotors operating in the air stream to operating within the sheltered wing structure. A louver system in the wing structure allows air to freely flow through the wing structure during the lift-off or hovering modes of the helicopter. The entire wing structure and rotors can be maneuvered as a unit so that the flight characteristics are similar to a conventional helicopter.
An example of a rotorcraft propelled by counter-rotating rotors is disclosed in U.S. Pat. No. 5,064,143 issued to Bucher. The rotorcraft has a pair of rotors driven to counter-rotate within a housing. The housing has adjustable air guiding discuss for the rotor stream and an airfoil-like outer shape to generate lift at horizontal flight. The air guiding devices include a circular arrangement of a plurality of individual sectors having tangentially extending blades arranged in a zone below the rotors. In each sector the blades are adjustable in their position relative to the rotor stream. In at least some of the sectors, the blade are arranged in pairs for an adjusting movement in opposite relative sense. The air guiding devices permit the pilot to control maneuvering of the rotorcraft.
Another example of a rotorcraft propelled by counter-rotating rotors is disclosed in U.S. Pat. No. 6,293,492 issued to Yanagisawa. The one-man rotorcraft has a drive transmission which transmits power from an engine to the upper and lower rotors comprised of respective first and second planet gear mechanisms provided with a common carrier. When the common carrier is rotated by an electric motor, a differential motion is generated between the two planet gear mechanisms which results in the rotors being rotated at different velocities to control yaw of the rotorcraft. A fore-and-aft swing mechanism and right-and-left swing mechanism depend from a lower end of a vertical shaft on which the rotors are supported. Moving a downwardly dependent control stick forward, backward, and side-to-side tilts the vertical shaft in the desired orientation per pilot input to the control stick to maneuver the rotorcraft. The control stick returns to a neutral position when subjected to a controlling force by the pilot.
Other types of aircraft have been developed as well. One example is in U.S. Pat. No. 6,113,029 issued to Salinas wherein is disclosed an aircraft capable of hovering and conventional flight. Vertical lift in the aircraft is produced by driving a column of air downwardly through an annular thrust flow channel formed in a fuselage of the aircraft. The fuselage has an aerodynamic shape which produces lift during forward flight like a conventional wing. The thrust flow channel has a flow control mechanism which directs the air flow according to pilot input between a vertical orientation to provide vertical lift during hovering flight and an angled orientation to provide both the vertical lift and a horizontal thrust for producing forward, rearward, and side-to-side flight.
In U.S. Pat. No. 6,254,032 issued to Bucher is disclosed an aircraft having a central cabin disposed in the center of a circular wing. Several electric drive units with rotors are pivotally disposed in an annular gap between the cabin and the ring. The drive units are pivoted downwardly to provide vertical lift and pivoted more horizontally to generate both lift and forward thrust. Attitude and movements of the aircraft are controlled by individual or group adjustment of the pivotal position of the drive units and rotors.
The major problem with the prior art helicopters, rotorcrafts, and other aircraft is the lack of controllability. None of the prior art helicopters, rotorcrafts, and aircraft are capable of flight in all six degrees of freedom or combinations thereof. This means all of the possible flight movements of: 1) pitch; 2) roll; 3) yaw; 4) up/down; 5) forward/rear; and 6) left/right. Therefore, maneuvering is always a compromise based on the performance capabilities of the particular helicopter, rotorcraft, or aircraft. This is particularly critical where flying space is at a premium such as during low hovers and flight adjacent obstructions such as buildings, bridges, towers, and sides of mountains.
There are a number of other problems with the prior art helicopters, rotorcrafts, and other aircraft, depending on the particular type of craft involved. For example, in helicopters and some rotorcraft the pitch control mechanism required to change the pitch of the main rotor blades is very complex and prone to mechanical failure, and excessive stresses are sometimes placed on the main rotor shaft, the pitch control mechanism, and the rotor blades during flight maneuvers which is also a source of mechanical failure. All such prior art helicopters, rotorcrafts, and other aircraft to varying degrees are difficult to control due to the large volume of air, or downwash, pushed downwardly by the rotor blades which causes excessive air turbulence which requires constant corrections and compensation for the turbulence. This is particularly troublesome when the downwash of the rotor blades is directed onto a closely disposed surface such as during take-off, landing, and hovering close to the ground, and maneuvering by the side of a vertical structure such as buildings or a mountain such as during mountain rescue work. This is also troublesome when flying through the downwash of the helicopters, rotorcrafts, or other aircraft. Finally, the cabin of a helicopter must be relatively small and streamlined to minimize drag from the downwash produced by the blades of the main rotor.
There is a need for a rotorcraft which solves these problems with prior art helicopters, rotorcrafts, and other aircraft.